The present disclosure relates to magnetic flowmeters, and in particular, to vapor permeation in a magnetic flowmeter.
In general, electromagnetic flow measurement techniques are applicable to water-based fluids, ionic solutions and other conducting flows. Specific uses include water treatment facilities, high-purity pharmaceutical manufacturing, hygienic food and beverage production, and chemical processing, including hazardous and corrosive process flows. Magnetic flowmeters are also employed in the hydrocarbon fuel industry, including hydraulic fracturing techniques utilizing abrasive and corrosive slurries, and in other hydrocarbon extraction and processing methods.
Magnetic flowmeters (or mag meters) measure flow by Faraday induction, an electromagnetic effect. The meter energizes a coil to generate a magnetic field across a pipe section, and the magnetic field induces an electromotive force (EMF) across the process flow. The resulting potential difference (or voltage) is measured using a pair of electrodes that extend through the pipe section and into contact with the process flow, or via capacitive coupling. The flow velocity is proportional to the induced EMF, and the volumetric flow rate is proportional to the flow velocity and flow area.
The coil and the electrode can be located in a hermetically sealed magnetics compartment in order to prevent damage to the electronics. However, a non-conductive liner lines the pipe section, and permeation of the liner can occur. In the event that permeation is occurring, vapor can build up in the magnetics compartment, increasing the relative humidity in the compartment. When the relative humidity reaches 100%, water droplets will form and can cause the magnetic flowmeter to fail due to the moisture shorting the electronics, such as the electrodes or the coil. Magnetic flowmeter failure is typically not noticeable until a short occurs and the flowmeter needs to be replaced.